Question

Find the value of: cos(theta-pi)​​

Answer 1

Step-by-step explanation:

$\cos( \theta - \pi) \\ \\ we \: \: can \: \: write \: \: this \: \: as \: \: \\ \\ \cos( - (\pi- \theta )) \\ \\ for \: \: cos \\ \\ \cos( - ( \pi - \theta ) ) = \cos(\pi - \theta ) \\ \\ and \: \: cos(\pi - \theta ) = \cos( \theta) \\ \\ so \: \: ans \: \: is \: \\ \\ \cos( \theta )$

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Answer 2

Step-by-step explanation:

We use the Formula #: cos(A+B)=cosAcosB-sinAsinB#

Letting, #A=, &, B=pi#, we get,

#cos(x+pi)=cosxcospi-sinxsinpi#

Since, #cospi=-1, and, sinpi=0#,

#cos(x+pi)=-cosx#.